The present invention relates to lock nuts having a plurality of resilient locking segments which deflect in a manner similar to that of a beam, and, more particularly, to a construction of the locking segments wherein the internal threads at the junction of adjacent beams are angled radially inward, thereby forming a V-shaped internal slot. The present invention also is directed to a new method of manufacturing the lock nut.
The present invention is an improvement in the design of a locking beam nut described and disclosed in U.S. Pat. No. 5,088,868. The locking beam nut of the ""868 patent discloses a design having a plurality of circumferentially-spaced resilient locking beams that were specifically configured to prevent any accumulated debris from preventing a desired deflection of the beams. The beams project from a substantially rigid body and have a circular opening extending completely through the body and the locking beams. The beams all taper inwardly, such that the circular opening they define have a uniformly-decreasing diameter. Continuous threads of substantially uniform depth are defined in the aligned openings, for receiving an externally threaded member, wherein the locking beams resiliently deflect outwardly to lock the member in place. The confronting sidewalls of adjacent beams are configured to diverge outwardly from each other, such that any debris located between them could not inhibit inward deflection of the beams upon removal of the externally threaded member.
Although the design described in the ""868 patent was an improvement upon prevailing locking beam nut designs, all previous designs for slotted beam nuts possess beams that are curved which, through natural stiffening of a curved design of a beam, have a tendency to concentrate loads and cause stress risers at the attachment points of the beams to the body of the nut. Consequently, low reuse cycles and rapid deterioration of the prevailing torque is undesirable. Another problem with previous beam nut designs is that typically the nut, which is utilized with a bolt having a holdout spring, compresses the spring when rotated in the internal threads of the beam nut. Periodically, the flexible holdout spring can become wedged and locked in two axial slots located on the inside diameter of the beam nut. Additional problems of prior designs are that the locking torque was insufficient and manufacturing and fabrication operations were extremely high due to the slotting, tapping and subsequent retapping operations necessary to remove burrs. Consequently, an improved beam nut design is necessary to address these and other problems associated with prior beam nut configurations.
The present invention provides a beam nut construction and arrangement which addresses the problems associated with prior beam nut configurations. The invention is embodied in a locking beam nut having a plurality of circumferentially-spaced resilient locking beams that are specifically configured to improve the performance and quality of the nut, and at the same time reduce manufacturing fabrication costs. The nut has unique features that provide substantially higher reuse cycles without rapid deterioration of the prevailing torque. The design allows for high reuse by lowering and reducing stress concentrations of a deflecting beam. The beam nut design of the present invention utilizes flat beams on the exterior portion of each beam, and a unique inside surface to substantially distribute the bending load through the length much more evenly, thus reducing stress concentrations. This is accomplished by incorporating an inside surface configuration wherein the internal threads at the junction of adjacent slotted beams are angled radially inwardly. This is in stark contrast to previous designs where the threads were 90xc2x0 to the slotted beams. The angled radially inwardly inside beam configuration provides for a substantially xe2x80x9cV-shapedxe2x80x9d internal slot length that travels the full length of the beam, and, in certain applications can continue through the entire length of the nut. The V-shaped internal slot has the capability to improve cycle life or reusability performance due to the fact that the cantilevered beam now approaches the characteristics of a true rectangular beam.
The internal V-shaped slot also eliminates the probability of the holdout spring on the bolt from becoming wedged into the slot by supplying an angled slope wide enough to act as a detent and not capture the holdout spring. A secondary locking system is added to provide additional prevailing torque and is accomplished during installation and removal of the beam nut wherein the holdout spring ratchets into each beam V-shaped slot whereby the additional friction contributes to increased prevailing torque.
A significant manufacturing improvement is realized with the internal V-shaped slot by streamlining and removing a series of costly operations in producing the beam nut previously required. The invention is produced by utilizing a heading procedure to form V-shaped slots from the exterior surface of a nut blank facing inward toward an external flat beam surface. Next a tap drilling operation commences wherein the tap drill removes the core and the apex of the external V form thereby forming the individual beams. The internal V-shaped slots are then formed by a broaching procedure and the nut is then threaded to complete the manufacturing process. This is in stark contrast to prior systems which required the tapping of the internal threads, then a slotting operation to form individual beams, which resulted in burrs forming in the internal threads of the nut. A subsequent retapping operation was necessary to remove the burrs. The method for manufacturing the present invention eliminates the beam slotting operation, double tapping and the deburring operations.
Other features and advantages of the present invention will be appreciated from the following description of an exemplary embodiment, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention.